Vector Surveillance

Vector surveillance is systematic monitoring of the seasonality and abundance of vector population.

The main purpose of dengue vector surveillance (larva, pupae and adult) is to obtain information regarding dengue vector density, which can be used to predict outbreaks and control dengue transmission.Vector surveillance is important…(1). To monitor vector densities over time enabling early warning and forecasting potential outbreaks/ epidemics. This facilitates initiation of early measures to prevent / control outbreaks

(2).To study the ecology, biology and bionomics of dengue vectors, in order to collect information on vector breeding sites, biting and resting habits, role played by individual vector species in disease transmission. This information is important for the implementation of an effective dengue control programme in the country.

Vector surveillance is carried out by the NDCU in cooperation with Anti Malaria Campaign (AMC), Anti Filariasis Campaign (AFC) and Medical Research Institute (MRI). In addition to central level offices, these institutions have their district level offices headed by Regional Malaria/ Medical officers (RMOO), Medical officers of AFC or Entomologist who are responsible for planning, implementation, monitoring and evaluation of entomological surveillance at the district level. Currently, 107 entomological teams are deployed for entomological surveillance at the central and district level offices of the AMC, AFC and MRI.

Vector Control

Vector Control activities are managed and conducted by the Medical Officer of Health (MOH) offices in the country with the collaboration of respective Regional Malaria/ Medical officers (RMO) Medical officer AFC and entomologists.

Major Activities

Facilitating district and divisional level vector management staff to perform optimally for the elimination/control dengue vectors by providing technical guidance, training, equipment, logistics, insecticides, and other resources including funding

Development and distribution of training manuals & guidelines on vector surveillance and control

Dengue Vector Control

In Sri Lanka, Aedes aegypti and Ae. albopictus are responsible for transmission of dengue and Dengue Haemorrahgic fever. These mosquitoes use a wide range of confined larval habitats, both man-made and natural. Some man-made container habitats produce large numbers of adult mosquitoes, whereas others are less productive. Current vector control measures used in Sri Lanka,

Environmental ManagementEnvironmental management is to change the environment to prevent or minimize vector breeding and/or man vector mosquito contact by destroying, altering, removing or recycling containers that produce larval habitats. Environmental management is the most efficient approach of dengue vector control and it is comprised of three components; i.e. Environmental modification, Environmental manipulation and changes to human habitation or behavior.

Environmental ModificationPermanent or long lasting physical transformation of vector breeding sites in order to eliminate/ reduce vector larval habitats.e.g. Provision of reliable water supply to the community in order to prevent water storageInstall a reliable water supply to the community and households would prevent or minimize water storage in cement tanks, barrels and other containers, thus, installation of a regular water supply would help a great deal to reduce dengue vector breeding in water storage containers and thereby reduce dengue transmission.

• Installation of mosquito proofing nets or tight lids to water storage tanks, barrels and other containersWater storage containers can be fitted with tight lids or tightly fitted mosquito proof mesh to prevent entering of mosquitoes to lay eggs (oviposition) in these containers. Studies have shown that such measures prevent mosquito breeding in water storage tanks and barrels in Sri Lanka

• Cleaning of blocked roof guttersClogged roof gutters are important breeding site of Ae. aegypti. The owners of the premises are required to clean or install them with a suitable angle in order to prevent water collection. If the owners are unable to maintain them satisfactorily, those gutters should be removed.

• Sheltering stored tyres in order to prevent collection of rain water in tyres• Proper disposal or recycling of discarded containers including tyresNon biodegradable items of household, community and industries should be collected and disposed regularly, preferably, once in 3 days.

Discourage growing plants that collect water in the leaf axils

Changes to human habitations or behaviourInstalling mosquito proof screens on windows, doors and other entry pointsUse of mosquito nets while sleeping during day time

Biological ControlBiological control is based on the introduction of organisms that prey upon, parasitise, competes with or otherwise reduce vector species.

Organisms.• The introduction of organisms that, parasitize, compete with or reduce populations of Aedes mosquitoes• Predators – can be deletedCurrently using biological agents for dengue vector controlLavivarous fish: Larvivorous fish can be applied for water storage tanks, barrels, cement lined wells and industrial tanks. Most efficient larvivorous fish for mosquito control are

Chemical methods for dengue vector control: LarvicidesChemical larviciding should be considered as complementary to environmental management. Except in emergencies, chemical larviciding should be restricted to containers that cannot otherwise be eliminated or managed. Currently, temephos 1% sand granules at the rate of 1g/ 10 liter of water is used for larval control in water storage containers such as tanks and barrels.

Chemical methods for dengue vector control: adulticidesIn Sri Lanka, space spraying (fogging) is widely used for dengue vector control. However, space spraying is recommended for vector control only in emergency situations to suppress ongoing epidemics or to prevent an incipient one. The objective of space spraying is the massive, rapid distruction of adult vector populations, both indoors and outdoors. In space spraying, a suitable insecticide is mixed with kerosene oil and released to the environment in the form of very tiny droplets. Once these droplets get contacted with the vector mosquitoes, the mosquitoes get knocked down and die. In order for the fog to reach the interior of the premises, the doors and windows should be kept open while fogging, however, food and water should be kept covered to prevent contamination with the insecticide.

Intersectoral collaboration and social mobilizationAedes aegypti and A. albopictus breed in and around human habitations.In addition to the house holds, these mosquitoes are frequently find in schools, offices, private institutions, religious places, bus depots, tyre shops etc. Thus, involvement of other sectors such as education, security forces, religious leaders, water board, road authority etc are of utmost importance for dengue prevention and control. Involving the other sectors for dengue vector control facilitate a more coordinated approach than the individual and independent efforts of different sectors. This also provides a platform for partners to resolve cross agency issues and to share best practices while reducing duplication of efforts.